Ink-jet printing systems commonly utilize either direct printing or offset printing architecture. In a typical direct printing system, ink is ejected from jets in the print head directly onto the final receiving medium. In an offset printing system, the print head jets the ink onto an intermediate transfer surface, such as a liquid layer on a drum. The final receiving medium is then brought into contact with the intermediate transfer surface and the ink image is transferred and fused or fixed to the medium.
In some direct and offset printing systems, the print head moves relative to the final receiving medium or the intermediate transfer surface in two dimensions as the print head jets are fired. Typically, the print head is translated along an X-axis while the final receiving medium/intermediate transfer surface is moved along a Y-axis. In this manner, the print head "scans" over the print medium and forms a dot-matrix image by selectively depositing ink drops at specific locations on the medium.
As the size of the desired image increases, the X-axis movement/head translation and/or Y-axis motion requirements become greater. One technique for printing larger-format images is disclosed in co-pending application Ser. No. 08/757,366 for IMAGE DEPOSITION METHOD, assigned to the assignee of the present application. This application discloses a method for interleaving or stitching together multiple image portions to form a larger composite image. Each of the image portions is deposited with a separate X-axis translation of the print head. After the deposition of each image portion, the print head is moved without firing the jets to the start position for the next image portion. Adjacent image portions overlap and are interleaved at a seam to form the composite image.
In this image deposition method, the relative position of each image portion must be carefully controlled to avoid visible artifacts at the seam joining adjacent image portions. With specific regard to the X-axis movement of the print head, it is necessary to precisely deposit each image portion such that adjacent image portions are aligned to properly interleave at the seam. It is also periodically necessary to move or tilt the print head away from the image-receiving drum to provide clearance for head maintenance operations such as purging, wiping and flushing, to thermally isolate the print head from the drum during non-printing periods and to provide a configuration that is resistant to shipping damage.
Prior art print head positioners have utilized various mechanisms to move a print head away from an image-receiving medium. An exemplary patent directed to a print head positioning apparatus is U.S. Pat. No. 5,608,430 for PRINTER PRINT HEAD POSITIONING APPARATUS AND METHOD (the '430 patent), assigned to the assignee of the present application. This patent discloses a print head tilt angle positioner that utilizes a tilt arm and a print head that are affixed to a shaft. The tilt arm rotates the shaft to move the attached print head away from the image receiving drum. To translate the print head laterally in the X-axis direction parallel to the drum, the entire shaft and attached tilt angle positioner mechanism are moved laterally. As the print head disclosed in the '430 patent is substantially the same width as the widest image to be printed, the shaft and attached print head and tilt angle positioner mechanism are required to translate only approximately 10 mm.
While the tilt angle positioner of the '430 patent provides highly accurate and repeatable positioning of a print head, it is less desirable for printers that require greater head translation distances for printing larger-format images. The rigid coupling of the tilt angle positioner to the shaft and attached print head creates a parasitic load on the lateral X-axis drive system that could potentially create undesirable image artifacts, especially as the print head translation distances along the X-axis increase.
The present invention is directed to a print head positioner that is uncoupled from the X-axis drive mechanism during imaging. The print head positioner includes a print head tilt mechanism that selectively engages a carriage supporting the print head and moves the carriage and print head only when the carriage is in a home position. The print head positioner also includes interlocks to prevent inadvertent disengagement from the carriage during tilting and to limit tilting when the carriage is not in the home position.